I. Field of the Invention
The present invention relates generally to fluid dispensing mechanisms and, more particularly, to an improved dispenser of simplified construction which does not require seals, particularly sliding seals, or springs for its operation, yet applies precisely controlled quantities of the fluid to a receiving surface.
II. Description of the Prior Art
There are a number of known designs for dispensing fluids such as adhesives, sealants, and the like, at accurately controlled flow rates, in accurate quantities, and for accurate placement on a receiving surface.
In one instance, a spring biased piston is pneumatically operated to open and close a valve, as needed, to control the flow of fluid to be dispensed from an outlet nozzle. The piston is provided with seals to prevent flow of the fluid in directions other than through the valve and these seals are subject to deterioration and wear, particularly when the fluid being dispensed is heated.
In another known dispenser design, a diaphragm is pneumatically operable to allow or interrupt flow of the fluid to a dispensing nozzle. The diaphragm can be moved by an actuating rod between a bowed position enabling flow to occur between inlet and outlet conduits and a planar position interrupting such flow. Again, proper sealing of the valve is a continuing problem. Specifically, it has not been possible heretofore to adequately seal the unit to prevent flow of the fluid into the actuating mechanism regardless of the type or number of seals being employed by the mechanism.
Another type of dispenser utilizes a positive displacement type of valve in which a quantity of the fluid is admitted into a chamber whereupon a piston then forces that quantity out through the dispensing outlet or nozzle. Again, in this instance, seals are necessary components of the mechanism and are not totally effective in satisfying their intended purpose.
In each of the foregoing instances, loss of the fluid that does not issue from the outlet nozzle but finds its way instead into other cavities of the dispensing mechanism is not the primary concern. Rather, when the fluid is a sealant or adhesive material, it subsequently accumulates, then hardens, and thereby has a detrimental effect on the operation of the dispensing mechanism, even to the point of rendering it inoperative.
Yet another known design of fluid dispenser utilizes a pinch valve according to which an actuator is selectively moved into or out of engagement with flexible tubing which extends from a source of supply to the dispensing head. While seals are not a particular problem with this design of dispenser, the length of the tubing necessary for this design is sufficiently long that it undesirably results in a delayed response time between the operation of the valve and the resultant flow of fluid being dispensed from the nozzle. This, in turn, causes inconsistent flow through the nozzle thereby reducing accuracy, namely, placement of a particular quantity of fluid at a particular location at a particular time.